1. Field
The present embodiment relates to a filter circuit and a semiconductor device including a filter circuit which may include a calibration function of a filter circuit.
2. Description of the Related Art
In a communication semiconductor device, a demodulated signal greatly deviates from an ideal signal since characteristics of a filter in an IF circuit which processes a received signal vary due to manufacturing processes, and this worsens a bit error rate and thus necessitates the calibration of the characteristics of the filter.
As a conventional art to calibrate characteristics of a filter, there has been known a method in which an oscillation circuit is formed by using a replica circuit of the filter, characteristics of the replica circuit are controlled so that the oscillation circuit has a constant oscillation frequency, and the characteristics of the filter are controlled similarly to the characteristics of the replica circuit (first conventional art: see, for example, Japanese Unexamined Patent Application Publication No. 2002-100962, and P. Quinlan et al., “A Multimode 0.3-200-kb/s Transceiver for the 433/868/915-MHz Bands in 0.25-μm CMOS”, IEEE J. Solid-State Circuits, vol. 39, no. 12, December 2004). As another conventional art, there has been known a method in which characteristics of a filter are controlled so that a delay time of a circuit including the filter becomes constant (second conventional art: see, for example, Japanese Unexamined Patent Application Publication No. 2006-287900). As still another conventional art, there has been known a method in which a band-pass filter functions as a closed-loop oscillation circuit and characteristics of the band-pass filter are controlled so that the oscillation circuit has a constant oscillation frequency (third conventional art: see, for example, Japanese Unexamined Patent Application Publication No. 2001-274654).
In the first conventional art, due to the need for providing the replica circuit, chip size and power consumption of a semiconductor device having the filter mounted thereon increases. Further, since the characteristics of the filter are controlled based on information which is indirectly obtained by using the replica circuit, calibration accuracy is lower than when the characteristics of the filter are controlled based on information directly obtained from the filter.
In the second conventional art, delay time measurement is used, but when a digital circuit is operated by the same clock frequency, the use of the delay time measurement results in lowered calibration accuracy since it is more difficult to highly accurately execute the delay time measurement than to execute the frequency measurement. There is another problem that this art is not directly applicable to a complex band-pass filter.
In the third conventional art, a center frequency and a Q-value of the band-pass filter, which determine the frequency characteristics of the band-pass filter, have to be separately calibrated since a gain and the Q-value of the band-pass filter need to have a proportional relation. Further, an amplitude detection circuit has to be provided to calibrate the Q-value of the band-pass filter, which increases circuit scale of the band-pass filter.